Tracking Tag Management Tool

Does anyone have a recommendation for a tag management tool? As we continue to expand our online marketing efforts, we find that we are constantly asked to add more and more tracking tags to our web pages. I have heard that there are reputable tag management tools out there, but would like some advice on which way to turn. Currently, we use Webtrends, Google Analytics, Doubleclick, Click Equations, and are considering adding Yahoo Analytics and other tags, but want to explore a tool that would allow us to place only one tag on our website that would reference a file that houses the remainder of the tracking tags. Any advice would be appreciated! Best, Rachel Jeske